Faculty Profile

Cranford, Ted W.

I am interested in questions of functional morphology (broadly defined) and in understanding patterns of morphologic change in evolution. Marine mammals offer exemplary comparative models for questions about mammalian anatomy and physiology. In the transition from a terrestrial to an aquatic existence, marine mammals were modified such that they now provide valuable contrasts with terrestrial or aerial mammals, and with other large aquatic vertebrates. The physical demands imposed by the aquatic environment have pushed marine mammals toward extreme adaptations in locomotion, thermoregulation, metabolism, respiration, pressure regulation and echolocation, to name just a few.

My work focuses primarily upon the functional morphology of biosonar, particularly sound generation and transmission, but also sound reception in toothed whales. I like to combine technological tools and with traditional anatomic techniques to develope new or innovative methods to interrogate the structure/function complex. This combination of methods enables me to answer questions about the origin and evolution of biosonar in toothed whales.

The cephalic anatomy of sperm whales is an interesting case because it provides an extreme morphologic example that helps define the range, limits, and context within which to evaluate pattern variation. For example, in small and medium sized odontocetes, the nose functions in sound generation and beam formation. By contrast, even though the sperm whale is the largest odontocete, its nose is many times larger than predicted by body size comparisons with other toothed whales. What do patterns in odontocete nasal anatomy tell us about the function and evolution of the world's largest nose? I attempted to address this question by using a giant CT scanner, originally designed to inspect solid-fuel rocket motors, to scan the head of a sperm whale.

After scanning the head of a sperm whale, I subsequently reconstructed it using 3-D computer graphics tools to gain virtual access to the internal in situ anatomic geometry. Some images and animations of the anatomy in the sperm whale's head can be found on my website:

These results strongly suggest that the enormity and complexity of the sperm whale's nasal apparatus evolved in response to sexual selection via an acoustic display (Cranford 1999). Since then, we have gathered similar data for a variety of whales. Analysis of these data will yield intriguing results.

In the most intriguing current example, we have used the data gleaned from CT scans of an adult male Cuvierís Beaked Whale (Ziphius cavirostris) head to produce the first quantitative description of the anatomy (Cranford et al., 2008a). We then used the foundation of that anatomic geometry to build a computer model that allows us to simulate sound propagating into or out of the head (Cranford et al., 2008b). The first set of simulations indicate that sounds enter the head by a previously unknown pathway, and suggests that this may be the pathway that was used by the ancient whales as far back as the Eocene.

My colleagues and I have also measured physiologic parameters from within the noses of bottlenose dolphins during the generation of sonar signals. We have simultaneously measured: (1) internal nasal air pressure using small digital catheters, (2) tissue motion using high-speed video endoscopy, and (3) acoustic pressure records from dolphins trained to perform target discrimination tasks by echolocation. This work has helped define the limits on the performance of dolphin biosonar. As an example, we discovered that bottlenose dolphins possess at least two sonar signal generators within their nasal apparatus, which helps explain limits on acoustic parameters such as, pulse repetition rate, signal bandwidth, frequency composition, and the geometry of the projected sonar beam.

A news brief about these results can be found in an article in Science News by Rachel Ehrenberg, entitled "Whales Drink Sounds: Hearing my use an ancient path." Science News, 173(6):84, 9 February 2008. (pdf)